Don't crash app on convert error.

[ego]

I have no idea what values we can choose as dummy, but let's doing the job!

File "pdf2docx/common/share.py", line 162, in <listcomp>
    return [int(s[i:i+2], 16) for i in [0, 2, 4]]
            ^^^^^^^^^^^^^^^^^
ValueError: invalid literal for int() with base 16: 'xe'